But the logic behind the inevitable dominance of Windows 8, as laid out by blogger Ville Aho, is wrong.

Here's the paragraph:

If we really are moving towards a post-PC world then doesn’t that mean that eventually mobile operating systems will replace desktop operating systems? And if so, isn’t it realistic to assume that the fittest, the most popular, the one with the biggest developer support and the largest ecosystem would be the one that would be the most attractive to the consumers also in the future? When comparing together all the operating systems on the market today: Mac OS X has about 5% of the market, iOS has 2%, Linux is at 1% and Android is at just 0.5%. Although iOS and Android seem to be the hot topics of the day, the fact is that Windows with its 90% market share is still dominating the market left, right and center.

Windows might still have 90% market share if you include all computer systems sold throughout the history of time.

But developers don't build for installed base alone. They also look at which platforms are shipping in the biggest volumes now. That's where the users are going to be. That's where the growth and opportunity is.

And where Aho really misses the boat is his assumption that only tablets are replacing PCs. That's not true. In the post-PC world, smartphones are computers. People work on them. IT departments plan for them and manage them. And most important, developers build apps for them.

So if you take smartphones into account, the REAL market share percentages for last quarter are something like this (math explained below*):

Windows: 85 million units, or 40% market share

Android: 74 million units, or 35% market share (fragmented among several different variants, but most apps can be made compatible with most Android devices with a little extra work)

iOS: 47 million units, or 22% market share

Mac OS X: 4 million units, or 2% market share.

(This is a rough estimate. In particular, there are other platforms, like Windows Phone and Linux desktops, whose market share is so low we didn't include them.)

So if you're a developer making apps today, are you really going to focus on Windows?

We don't think so. And most developers who are targeting a market today are starting with mobile -- iOS first because that's where the biggest spenders are, Android second. Beyond that, it's mostly Web apps. Making apps for Windows is kind of an anachronism anymore,

Later, Aho writes:

If we really are moving towards a post-PC world, wouldn’t that mean that all the millions of PCs from countless different manufacturers, offered at every possible price point and sold literally everywhere would in the future, more or less, be replaced by tablet computers? Is there anything that would suggest that around 90% of these computers would not be continuing to ship with Windows?

Yes. The world has changed. Smartphones are personal computers, and Windows is no longer the only computing platform that matters.

Apple sold 4 million Macs, so we have to cut those from the total, leaving 85 million (mostly) Windows PCs.

Apple sold 11.8 million iPads. But it also sold 35.1 million iPhones. That's about 47 million iOS devices. (Not including the iPod Touch, which is probably used more in a disconnected state as a music player than in a connected state as a computer, and is almost surely never used for work.)

We haven't yet seen any smartphone platform market share stats for Q1, so we're going to have to guess a little bit based on Q4 stats. Back then, Android had about 50% share, compared with about 23% for iOS (Gartner).

So let's assume the sales ratio of Android to iPhone remained about 2 to 1. That means about 70 million Android phones shipped in Q1.

What about Android tablets? Recent statistics from Good Technologies suggest that Android tablets make up less than 5% of total enterprise activations, but let's be generous and assume that there were lots of consumers buying Kindles and never taking them to work. So let's say 4 million Android tablets.